Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Sulfur dyes are the most commonly used dyes manufactured for cotton in terms of volume. They are cheap, generally have good wash-fastness and are easy to apply. The dyes are absorbed by cotton from a bath containing sodium sulfide or sodium hydrosulfite and are made insoluble within the fiber by oxidation. During this process these dyes form complex larger molecules which is the basis of their good wash-fastness. These dyes have good all round fastness except to chlorine. Due to the highly polluting nature of the dye-bath effluent, slowly sulfur dyes are being phased out.